1. Field of the Invention
The present invention relates to the field of wireless networks.
2. Discussion of Related Art
The wireless networks of today are homogeneous. There are many different types of wireless networks available today like mobile, such as the networks known as 2.5 G, 3 G etc., wireless LANs, such as the networks known as 802.11 and HIPERLAN, and short range wireless, such as the network known as Bluetooth, etc. However, there is no interoperability between these wireless networks. In other words, the user of one network is not able to seamlessly handover to another type of network. It is envisioned by the present invention that it will be possible in the future to seamlessly handover between heterogeneous networks. In such a heterogeneous environment there is need for mechanisms that allow seamless transition between different networks.
Traditionally, handovers between networks are initiated on the basis of the received signal strength, which is measured at the network and the mobile device. However, the present invention envisions that in the future heterogeneous environment the decision of when and where to handover will most often be made by application layer entities, especially in the case of vertical (intra-access technology) handovers.
In order to support such a seamless environment, the present invention requires mechanisms that allow devices to seamlessly handover between heterogeneous networks and allow services to adapt to changing network conditions. Although the present invention can encompass various techniques to realize the seamless handover, the description of the present invention focuses on the application level triggering mechanisms for seamless mobility.
A typical heterogeneous network environment 100 is schematically shown in FIG. 1. In particular, the network environment includes a mobile terminal, such as a cell phone 102, that is connected to an IP backbone 104 (Internet) through a wireless base station 106 and a Universal Mobile Telecommunications System (as identified in Europe)/WCDMA (as identified in Japan) network 108. In particular, the mobile terminal is first connected to the base station 106, then all traffic generated by the mobile terminal goes to the network 108 and goes out to the Internet. In a heterogeneous environment there will be many different base stations of different access technologies to which the mobile terminal 102 can possibly handover. As shown in FIG. 1, such a heterogeneous environment can include: 1) wireless base station 110 and a CDMA2000 network 112, 2) wireless base station 114 for Bluetooth network and 3) wireless base station 116 for a WLAN (IEEE 802.11A or IEEE 802.11B) network.
While it is possible to initiate the handover processor manually via the mobile terminal, it is preferred that a process is developed where the handover is done automatically. In the case of automatic handover, it is very important for the mobile terminal 102 to know when to do the handover and to which network in a heterogeneous environment such as shown in FIG. 1. It is known that the handover decision can be based on a number of factors. First, information about the network topology and target base stations is required. This may include information about the coverage areas of (geographically) nearby base stations, the type of services supported by the (handover) target base stations, the available bandwidth, available security mechanisms, QoS (Quality of Service) and cost associated with accessing the networks etc. Such information can be made available to the mobile device by a location server that continuously updates this information for base stations in a certain geographical region. It is also possible to determine network topology in the manner described in 1) F. Watanabe etc al., “Using subnet relations to conserve power in a wireless communication device,” currently apply to IPR and 2) G. Wu, P. J. M. Havinga, and M. Mizuno, “MIRAI architecture for heterogeneous network,” IEEE Commun. Mag., February 2002.
A second factor to consider is that some information is locally available on the mobile device. Such information can include information about the geographical location of the mobile device, signal strength with the current point of attachment, signal strength of the target network, type of applications that are running along with application specific, QoS, bandwidth, security requirements and battery consumption level etc.
A third factor to consider is that user context information is required in order to make effective triggering decisions. This context information will include user preferences for services and networks depending on different factors such as location, time, nearby people, battery resources etc, information about user schedules/agendas, activity e.g. running, walking, driving a car etc and past usage behavior. This context information may be stored locally on the mobile device or it may reside on some database in the network. It should be noted that the Internet Engineering Task Force (IETF) Seamoby working group has proposed an IP level context transfer along the forwarding path of a mobile node in order to provide seamless mobility (see the charter archive maintained by the IETF. In its standardization efforts, Seamoby discusses AAA context transfer between AAA servers as the mobile terminal moves between different IP subnets. In addition, the IEEE802.11 Task Group f has standardized the inter-access point protocol, which will exchange user context information transfer between the new access point (AP) and the old AP (see IEEE Std 802.11f/D2.0, Draft Recommended Practice for Multi-Vendor Access Point Interoperability via an Inter-Access Point Protocol Across Distribution Systems Supporting IEEE802.11 Operation, July 2001). Note that the access point has a station functionality and provides access to the Intranet and the Internet via wireless medium.
A fourth factor is that the user may be running different services on the mobile terminal that need to adapt to the new network conditions. For example, a video conference between two mobile users on a cellular network will have different parameters as compared to a video conference between the same users if they handover to a wireless LAN network. Mobile IP guarantees session continuity but does not provide service adaptability. See the draft proposal by D. Johson and C. Perkins, “Mobility Support in IPv6,” available from the archive maintained by the IETF.
A fifth factor is that battery resources are very critical for a handheld device because of limited battery capacity. In the past a number of approaches have been adopted for enhancing battery performance as well as to make the applications themselves battery aware. In a heterogeneous environment there will be a large number of access networks that a mobile device can potentially connect to. Software Defined Radios may be the key enabling technology in providing this type of connectivity. See K. C. Chen, R. Prasad, H. V. Poor, “Software Radio,” IEEE Pers. Mag., vol. 6, no. 4, August 1999. The problem is how the mobile device knows when to scan for which access network types.
Based on the above-described systems, there is no technology at this time that can provide seamless handover to other networks in next generation wireless networks.